Why is if not success then is used?

so if not success then is sometimes used on other scripters, but why it is used? it is only used to know an error?

Here we set up for that situation:

local success, message = pcall(function()

	-- Let us say I have a script that does not need to work but I want to know if it fails in here

end)

if not success then

	print("Non crucial code failed error is: "..message)

end

This time I don't want to do anything if it is successful so I use if not success so that it only passes the if statement if there was a failure. I hope this helps and have a great day scripting!